1. Field of the Invention
The present invention generally relates to an electronic balance, in particular, to an electronic balance capable of weighing a desired number of to-be-measured objects by placing the to-be-measured objects with the same mass on a weighing pan.
The abovementioned “electronic balance” mainly refers to an electronic balance with an electromagnetic force balance mechanism, and a load cell type, tuning fork type, capacitance type electronic balance, as well as all the weighing devices for measuring and weighing by using a load weight of a to-be-measured object as an electric signal.
2. Description of Related Art
When an electronic balance is used for measuring an object, the to-be-measured object is placed on a weighing pan, and a weighing value shown in the display is read only after the vibration of the weighing pan caused by placing the object thereon is attenuated and stabilized. However, besides the vibration caused by placing the to-be-measured object on the weighing pan, the weighing pan may also generate continuous vibrations due to the surrounding environment (such as vibration of the base on which the electronic balance is disposed, and airflow change), and such continuous vibrations may not cease completely. If no measure is taken to prevent the vibrations of the electronic balance, when the displayed value is read, the weighing value shown in the display may vary due to the vibrations caused by the surrounding environment. As a result, it is difficult to read the displayed value.
Therefore, for some electronic balances, in order to stabilize the displayed weighing value for being read by a user, a moving average process is executed to calculate an average value of the latest weighing value data and a specified number of previous weighing value data obtained within a fixed period, so as to stabilize the displayed value (with reference to Patent Document 1).
The moving average process is executed to avoid the influences caused by the vibrations of the weighing pan, so as to realize a stable display. Generally, when the specified number of weighing value data maintains stable continuously, a sign (stability sign) for indicating a stable status is shown on the display, and the user can proceed weighing after confirming that the displayed stability sign.
If the moving average process is executed to stabilize the displayed weighing value, the stability of displayed weighing value is indeed improved. However, on the other aspect, the tracking and response capabilities to the load deteriorate. That is, when a dramatic load change occurs on the weighing pan and the moving average process is executed, the moving average process may not only cause noises as a vibration component, but also restrain the variation of the practical load change. Ultimately, the response to the load change slows down.
Therefore, when the moving average process is being executed, a threshold of the load change amplitude is preset as a criterion. Then, whether the moving average process is switched to “stop” or “start” is determined according to a comparison result between the practically produced load change and the preset threshold of the load change amplitude. That is, when the load applied to the weighing pan changes and during the period when the load change is greater than the preset threshold, the moving average process stops. When the load applied to the weighing pan changes and during the period when the load change is smaller than the preset threshold, the moving average process starts.
Furthermore, when the to-be-measured object is in a form of powder or liquid such as medicine, simply weighing a desired weight of the to-be-measured object is sufficient. When a powder object is being weighed, before the load of the powder reaches a target weight, the load of the to-be-measured object is continuously added onto the weighing pan for several times. As the weight on the weighing pan approaches the target weight, the increment of the load gradually reduces each time when the load is added onto the weighing pan. However, if the variation produced by one increment of the load fails to reach the preset threshold of the load change amplitude in the balance, the moving average process maintains, and the response to the added load slows down. Accordingly, some patents have disclosed the following situations. Whether a weighing operation is performed or not according to the threshold of the load change amplitude and a load change rate threshold is determined When the weighing operation is performed in order not to execute the moving average process before the added load gets smaller to improve the response capability, the threshold of the load change amplitude is altered to a small value, and the calculation operations of the moving average process stop before reaching the threshold. Hence, a measurement with a preferred response capability is performed. On the other aspect, if the load change rate is determined to be smaller than the load change rate threshold, and an additional load is not added for the weighing, the threshold of the load change amplitude recovers to a regular value, and the calculation operation of the moving average process is performed to improve the operation efficiency. Hence, the displaying stability is maintained (with reference to Patent Document 2).
Patent Document 1: Japan Patent Publication Gazette No. H11-311566
Patent Document 2: Japan Patent Publication Gazette No. 2006-84192